The success of commercial cellular networks based on GSM/WCDMA/CDMA radio access technologies etc. has lead to an increasing interest to also offer priority services or public safety services such as e.g. fire department, police networks, over these networks and in such way complement or replace existing dedicated public safety networks and technologies such as TErrestrial Trunked RAdio (TETRA), by European Telecommunications Standards Institute (ETSI), or other professional mobile radio systems. Given also the introduction of new cellular radio access technologies such as Long Term Evolution (LTE) and the evolution of existing cellular networks towards offering mobile broadband services it is also of interest to extent the scope of priority services to not include only voice services but also to include Internet Protocol (IP) and multimedia based services such as e.g. Video calls, Push to talk, Voice over IP.
The 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations, to make a globally applicable third generation (3G) mobile phone system specification within the scope of the International Mobile Telecommunications-2000 project of the International Telecommunication Union (ITU). 3GPP specifications are based on evolved Global System for Mobile Communications (GSM) specifications. 3GPP standardization encompasses Radio, Core Network and Service architecture.
Specific requirements on 3GPP access are specified, which need to be fulfilled to support multimedia priority services. These requirements are inline with requirements in other standardization bodies or governmental agencies such as Government Emergency Telecommunications Service (GETS). GETS is a White House-directed emergency phone service provided by a division of the Department of Homeland Security. GETS uses enhancements based on existing commercial technology.
Multimedia priority services put requirements on the networks to support multiple priority levels and to ensure that priority users are prioritized when it comes to access to radio resource over other non-priority users e.g. commercial users. Furthermore, it is required that the network support queuing at congestion in scenarios where pre-emption of lower priority users resources are not possible or allowed for commercial or regulatory purposes.
In order to support fair and strict priority queuing at radio resource congestion in the 3GPP networks it is required that the priority queuing mechanism is implemented close to the radio network where the radio resource congestion occurs. Queuing at application level will make it difficult to guarantee fairness between different users since the application server will not be aware of the congestions on the radio cell level.
Basic support for queuing for setup of Radio Access Bearers (RAB) in the Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS) Terrestrial
Radio Access Network (UTRAN)/Wideband Code Division Multiple Access (WCDMA) is standardized. The purpose of this functionality in UTRAN is to allow the RNC to queue bearer requests for one user. The standardized functionality does not support fair priority queuing between different users and the queuing also is not maintained when an inter-RNC handover is performed since in this scenario all pending RAB request will need to be aborted.
For Circuit Switched (CS) services in GSM and UTRAN there is also support for queuing in the scope of enhanced Multi-Level Precedence and Pre-emption service (eMLPP). Also in this case will the queuing not support inter-Base station or inter-RNC handovers (HO).
Not maintaining queuing status at inter-BSC and inter-RNC handovers may be acceptable in existing GSM/UTRAN networks since the BSCs and RNCs cover a large area and inter-BSC/RNC handovers are rare. There is however a recent trend in cellular networks to use a more flat RAN architecture where there are no central coordinating node which owns the cell level resources. Instead the cell level resources are owned by the base station. LTE (E-UTRAN) radio access network is an example of a radio network using a flat architecture where the base station node (eNodeB or eNB) only serves a few cells. LTE is sometimes also referred to as Evolved UMTS Terrestrial Radio Access Network (E-UTRAN). Flat architectures are also possible for UTRAN and WiMAX networks. No queuing mechanism has been defined in LTE (E-UTRAN).
Current queuing mechanism as for instance defined in 3GPP does not support the case when the node performing the admission control, i.e. the cell resource owner, and maintaining the queuing is changed e.g. an inter-RNC handover. There is therefore a risk that the user session in such a queue would either be blocked or will loose its position in the queue. Since these types of handovers will be very frequent in LTE and other networks using a flat RAN architecture it will be difficult with the existing solutions to maintain a fair and strict priority queue in case of radio network congestion affecting multiple cells.
Currently it is specified that any pending bearer requests will be ignored or dropped for users experiencing inter-eNodeB handover. In this case it is required that the queued bearer request is re-requested from the MME in the new eNodeB however in this case the queuing time in the source eNodeB will not be known in the target eNodeB so the target eNodeB has no choice but to put the new request at the end of its queue (assuming the target cell is also congested). If the user then moves on to a new or old eNodeB before the pending bearer is setup the same process will be repeated again meaning that in theory the bearer request will be queued for a significantly longer time compared to if the user was stationary. This leads to unfairness between different users and will introduce some unpredictability in the queuing process which might mean that the queuing solution do not fulfill the requirements.